Pulse producing circuit arrangement



May 24, 1960 T. A. WATSON 2,938,148

PULSE PRODUCING CIRCUIT ARRANGEMENT Filed June 27, 1957 774. WATSON United States Patent 2,938,148 PULSE PRODUCING CIRCUIT ARRANGEMENT Thomas Arthur Watson, Montreal, Quebec, Canada, assignor to Canadian Marconi Company, Montreal, Quebee, Canada Filed June 27, 1957, Ser. No. 668,559 Claims priority, application Canada Oct. 26, 1956 1 Claim. (Cl. 315-230) This invention is concerned with pulse signalling circuits and aims to provide an arrangement which gives a unidirectional pulse output in response to a change of input signal frequency from a first predetermined value to a second predetermined value.

In some signalling systems, such as telephone systems, it is desired to produce a pulse in response to the changeover of a signal from a first to a second frequency. It is desirable that the system should not respond to amplitude variations or interruptions of the control signal, but only to the change from the first to the second frequency as aforesaid. This invention provides an arrangement for accomplishing this purpose in a simple, reliable and economical fashion. It makes possible a most desirable all-electronic equivalent to the polarized relays which have been used in the past for similar purposes.

According to the invention there is provided a pulse producing circuit arrangement comprising a source of signals variable between a first given frequency and a second given frequency; means to apply said signals concurrently to a first circuit responsive to said first frequency and to a second circuit responsive to said second frequency; first rectifier and filter means connected to said first circuit and adapted to develop at a first and a second terminal direct current potentials of equal magnitude and opposite polarity in response to signals of said first frequency; second rectifier and filter means connected'to said second circuit and adapted to develop at said first and second terminals direct current potentials of equal magnitude and opposite polarity in response to signals of said second frequency, said first and second rectifier and filter means being oppositely poled in respect to the potentials developed thereby at said first and second terminals; a pair of trigger triode gas discharge tubes connected in parallel across a source of direct current supply said pair of tubes having a common cathode resistor, individual and equal anode resistors, and individual charging capacitors connected between each anode and a point of reference potential; means connecting the grid of one of said tubes to said first terminal, means connecting the grid of the other said tubes to said second terminal; and utilization means fed from said common cathode resistor.

The invention will further be described with reference to the accompanying drawing which shows a preferred embodiment thereof.

The frequency changing input signal is applied to two frequency responsive circuits T and T indicated here as tuned transformers responsive respectively to the frequencies f and f When T or T responds to a signal it applies, via the rectifier systems Rect. 1, Rect. 2 or Rect. 3, Rect. 4, and the associated filter systems which may be, as shown, partly shared between the two transformer/rectifier arrangements, signals of the polarity shown to the terminals A and B. Thus an applied signal of frequency of 1, results in a positive voltage appearing at terminal A and a negative voltage appearing at terminal B whereas an applied signal of frequency 3 results in voltages of opposite polarity at A and B.

Considering now the tube circuiting involving V, and V These tubes are trigger triode gas discharge tubes,

2,938,148 Patented May 24, 1960 preferably of the miniature cold cathode type. The supply voltage, B+, is less than the anode to cathode breakdown voltage of these tubes but greater than that voltage required to maintain conduction once the tubes have been fired. Assume that V,,, say, is conducting and that V is not. The voltage at the anode of V will be the full supply voltage and C; will be fully charged. The value of the cathode resistor R is relatively low whereas R and R have relatively high values. Thus the voltage developed across R during normal tube conduction is low whereas R and R cause an appreciable reduction of the voltage appearing at the anode of a conducting tube.

Suppose now a signal of frequency f is applied. Terminal B will go positive, thus firing tube V C; 'will discharge rapidly through V and will momentarily raise the cathode potential of V Since the anode potential a V,, is already low due to the voltage drop in R and cannot be raised rapidly since to do so requires the charging of C the anode to cathode potential across V,, will drop and extinguish conduction in V As C7 becomes discharged the current through R falls to a low steady state value. Thus when conduction is switched between V, and V a positive pulse is produced across R which is available for application as desired.

It will be realised that an ouput pulse will be obtained only by a changeover in applied signal frequency since the tube circuit is essentially a bi-stable system, unresponsive to interruptions of an applied signal. By virtue of the bucking arrangement of the rectifiers of the two frequency selective circuits, noise present simultaneously in the two frequency spectrums balances out, and thus the system may be made basically immune to noise.

I claim:

A pulse producing circuit arrangement comprising a source of signals variable between a first given frequency and a second given frequency, a first selective circuit responsive to signals of said first frequency, a secondselective circuit responsive to circuits of said second frequency, means to apply signals from said source concurrently to said first and second selective circuits, a first rectifier system fed from said first selective circuit and adapted to develop a first pair of outputs of substantially equal and oppositely polarized D.C. potential in response to signals delivered to said first rectifier system from said first selective circuit, a second rectifier system fed from said second selective circuit and adapted to develop a second pair of outputs of substantially equal and oppositely polarized D.C. potential of amplitude substantially equal to that of said first pair of D.C. potential outputs in response to signals delivered to said second rectifier system from said second selective circuit, a pair of terminals, means to apply to each of said pair of terminals in opposite polarity an output from said first rectifier system and an output from said second rectifier system, a source of direct current supply, a pair of trigger triode gas discharge tubes connected in parallel across said source of direct current supply, said pair of tubes having a common cathode resistor, individual and equal anode resistors, and individual charging capacitors connected between each anode and a point of reference potential; means connecting the grid of one of said tubes to said first terminal, means connecting the grid of the other of said tubes to said second terminal; and utilization means fed from said common cathode resistor.

References Cited in the file of this patent UNITED STATES PATENTS 1,919,977 Fitzgerald July 25, 1933 1,947,093 Knowles Feb. 13, 1934 2,043,844 Teare June 9, 1936 2,605,449 Schrader July 29, 1952 

